In recent years, in order to implement multimedia communication, information transmission schemes have been in need whereby large volume of information such as data and image, as well as speech, can be transmitted with high reliability at high speed. In particular, when transmission is carried out under an environment such as a mobile wireless transmission path where multipath fading, shadowing and the like may occur, it is an important issue to deal with these problems.
As one of techniques to solve such a problem, there is an adaptive modulation technique for performing transmission and reception, changing a modulation scheme adaptively according to communication quality of the propagation path (for example, see Patent Document 1). The adaptive modulation technique disclosed in Patent Document 1 is directed to a TDMA-FDD (Time Division Multiple Access-Frequency Division Duplex) scheme, where a downlink to transmit signals from base stations to mobile stations and uplink to transmit signals from the mobile stations to the base stations are formed with time-division multiplexed channels with different frequencies, and each of the base stations and mobile stations estimates communication quality of a propagation path in a transmission frequency for the station from a received signal of the station, and determines a modulation scheme for the communicating party according to the estimation result. To be more specific, each of the base station and mobile station selects a modulation scheme that is able to keep a BER at equal to or smaller than a predetermined value and achieve the highest information transmission speed.
Further, as an example of the method of selecting a modulation scheme according to an estimation result of communication quality, there is a method where a transmitting side transmits a transmission signal to which error correction codes are added, and a receiving side selects a modulation scheme based on a bit error rate (BER: Bit Error Rate) detected in error correction processing based on the error correction codes (for example, see Patent Document 2).    Patent Document 1: Japanese Patent No. 3240262    Patent Document 2: Japanese Patent Application Laid-Open No. HEI9-200282